Note: Descriptions are shown in the official language in which they were submitted.
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t
~I~E, Pll'l '.~ u
~ v ~ N
Wire Cord for Reinforcing Rubber Items
The invention relates to a wire cord for reinforcing
rubber items, more particularly pneumatic tyres,
comprising at least three wire filaments arranged about
a continuous core filament.
Wire cords of this kind are known, they serving, more
particularly, for reinforcing pneumatic tyres such as,
for example, car and truck tyres. Such wire cord
inserts in tyres are known as belted cord inserts.
When employed in van and truck tyres such wire cord
inserts or strengthen:ings are subjected to higher
stresses than when used in car tyres, this being the
reason why the demands on wire cords reinforcing truck
tyres being higher. Accordingly, when cheap-production
steel cords having a si.mple configuration, as employed
for example in car tyres, are used in van and truck
tyres belt edge detachment may easily occur.
Such simply configured steel cords consist, for
example, of a core composed of three wire filaments
having a diameter of ().2 mm as well as six 0.35 mm
diameter wire filaments arranged about this core.
Producing such a steel cord is simple and in general
presents no problem in processing. As already
mentioned, however, due to its stiffness, detachment of
th.e belt edge may easily occur in the tyre, making the
tyre useless.
This risk of the belt edge becoming detached is
significantly diminished in the case of cords produced
at more expense having a higher number of wires (for
example steel cords having a core cord of three wire
fi.laments wrapped by nine wire filaments and a
sheathing ply of a furt:her fifteen wire filaments each
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having a diameter of 0.22 mm as well as a spiral wire
of 0.15 mm diameter surrounding this structure).
However, due to the geometric assignment of the
individual wires relative to each other inner cavities
automatically materialize in the case of such wire
cords having a higher wire number, it then no longer
being possible for the embedding rubber to penetrate
therein so that the adhesive bond of the embedding
rubber remains limited to the outer casing sections. On
top of this, moisture contained in the entrapped air
has a corrosive effect on the wire cords from within
and contributes towards the wires becoming prematurely
aged and ruined.
Known from DE 26 48 524 A1 is a wire cord as a medium
for strengthening rubber items which is configured of
three or more solid metal wires twisted together about
a continuous core of a non-metallic compressible
material. More particularly this non-metallic
compressible material is a vulcanizable rubber, a
thermoplastic, an aromatic polyamide or a natural or
man-made fiber material. By employing such a non-
metallic compressible rnaterial as the core of a wire
cord the vacant space otherwise existing in the wire
cord is practically or substantially filled out, as a
result of which displacements of individual outer wires
under the influence of lateral compressive forces are
avoided. Filling out the vacant spaces in the wire cord
in this way is achieved by the elastomer or textile
core yielding to the steel wires grouped about the core
when the steel cord is processed in the tyre so that
the steel wires are able to approximate each other and
slightly deform the core wire.
Known from DE-PS 816 308 is a reinforcing insert for
items made of rubber, t:he wire cords of which comprise
a non-vulcanized or prevulcanized rubber core in which
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the individual wires are located spaced away from each
other. Due to these rubber cores the cords are endowed
with a high elastic strain so that the wire cord
features higher flexibi]ity.
Known from DE-OS 2 209 752 are wire cords as
reinforcing inserts in conveyor belts consisting, for
example, of wire filaments arranged about an elastomer
core.
As compared to the above the invention is based on the
object of providing a wire cord of the aforementioned
kind which is simple in configuration and thus cost-
effective in production whilst, on the other hand,
ensuring good anchorage and location of the wire cord
edges in the rubber item to be reinforced with reduced
risk of corrosion in the interior of the wire cord.
To achieve this object in accordance with the invention
a wire cord is proposed for reinforcing rubber items,
more particularly pneumatic tyres, comprising at least
three wire filaments arranged about a continuous core
filament, the core filament consisting of a non-
metallic material capable of longitudinal contraction
when the rubber item to be reinforced is vulcanized. In
vulcanization of such a wire cord configured in
accordance with the invention longitudinal contraction
of the core filament forming the core of the wire cord
occurs, i.e. the core filament contracts in the
longitudinal direction of the wire cord, as a result of
which the core filament retracts from the cut edges of
the wire cord so that a cavity defined by the wire
filaments surrounding the core filament materializes
there. During vulcanizalion the rubber blend is able to
penetrate into this cavity as a result of which a
particularly good anchorage of the wire cord in the
rubber item to be reinforced is assured.
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In one advantageous aspect of the invention the core
filament consists of a non-drawn aliphatic polyamide,
preferably of non-drawn nylon. Non-drawn aliphatic
polyamide, more particularly, non-drawn nylon features
the advantage that when the rubber item to be
reinforced is vulcanized it shrinks not only
longitudinally but also the diameter of the aliphatic
polyamide simultaneously increases during the shrinkage
process. Due to this increase in the diameter the
polyamide penetrates int:o cavities existing between the
wire filaments surrounding the core filament and
practically fills the cavities out. When using non-
drawn aliphatic polyamide, more particularly, non-drawn
nylon as the core filament the wire cord in accordance
with the invention thus offers, on the one hand, the
advantage of better locating the wire cord cut edge in
the rubber item to be reinforced since the rubber blend
thereof is able to penetrate into cavities at the end
of the wire cord created by the shrunk polyamide core
whilst, on the other, the wire cord in accordance with
the invention offers l_he advantage that the shrunk
polyamide core retracts into the interior of the wire
cord where it fills out the cavities between the
individual wire filaments so that corrosion of the
individual wires from the interior of the wire cord is
avoided.
The invention will now be explained by way of an
example embodiment with respect to the drawing in which
Fig. 1 is a schematic illustration of a cross-section
through a wire cord in accordance with the
invention for reinforcing rubber items prior to
vulcanization of the rubber item to be reinforced.
Fig. 2 is a schematic illustration of the wire cord in
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accordance with the invention as shown in Fig.
after vulcanizat:ion of the rubber item to be
reinforced.
Fig. 3 is a schematic illustration of a section
through
the wire cord as shown in Fig. 2 after
vulcanization of the rubber item to be
reinforced
as taken along the section line III-III.
Referring now to Fig. 1 there is illustrated
schematically a cross-section through a wire cord 1 in
accordance with the invention for reinforcing rubber
items, more particularly, pneumatic tyres. The wire
cord 1 in accordance with the invention comprises a
core filament 3, about which six wire filaments 2 are
arranged symmetrically in parallel. In the example
shown both the wire filaments 2 and the core filament 3
each have the same diameter.
The diameter of the wire filaments 2 and of the core
filament 3 is selected as a function of the intended
future employment of the wire cord, i.e. depending on
the type and size of the tyre to be reinforced. In the
example embodiment illustrated the diameter may be, for
example, 0.35 mm, however, also others diameters are
possible. It will readily be appreciated, of course,
that that wire cords may also be employed in which the
wire filaments 2 and the core filament 3 differ in
diameter.
Due to the circular cross-section of the wire filament
2 and of the core filament 3 a cavity 4 is formed in
each case between two adjacent wire filaments 2 and the
core filament 3.
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In accordance with the invention the core filament 3 of
the wire cord 1 as shown in Fig. 1 is made of a non-
metallic material whic;h is capable of contracting
longitudinally in vulcanization of the rubber item to
be reinforced. This property is made use of to create
in the rubber item to be reinforced, more particularly
a pneumatic tyre, a firm anchorage of the wire cord.
For this purpose the wire cord 1 as illustrated - after
calandering and cutting the belt plies - is processed
into a so-called green tyre which is subsequently
vulcanized. In vulcanization the core filament 3
contracts longitudinal:Ly, i.e. it shrinks in the
direction of the longitudinal axis of the wire cord 1
towards its centerline (cf. Fig. 3), as a result of
which cavities are created at the cut edges 6 of the
wire cord 1 into which the vulcanization blend can
penetrate, thus resulting in intermeshing of the wire
cord, more particularly of its wire filaments 2 with
the rubber item to be reinforced.
Referring now to Fig. 2 there is illustrated a section
through the wire cord 1 in accordance with the
invention as shown in ~ig. 1 after vulcanization. Due
to its shrinkage the core filament 3 has not only
changed in length, its diameter has also increased at
the same time. This results in the core filament 3
expanding into the cavities 4 as described above,
practically filling them out. As evident from Fig. 2
the space enclosed by the circular arrangement of wire
filaments 2 is practica~Lly filled out completely by the
non-metallic material of the core filament 3 so that
substantially cavities no longer exist therein.
Due to substantially the complete space enclosed by the
wire filaments being filled out in accordance with the
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invention the risk of corrosion of the wire cord 1 from
within due to entrapped moisture is greatly reduced.
Referring now to Fig. 3 there is illustrated
schematically a section in the longitudinal direction
through the wire cord in accordance with the invention
as shown in Fig. 2 after vulcanization as viewed along
the section line III~ [. Fig. 3 shows the wire cord 1
in accordance with the invention in the embedded
condition in the rubber item 5 to be reinforced. The
rubber item 5, not shown in Fig. 2 to make for a better
overview, is shown in section in Fig. 3. The rubber
item 5 to be reinforced in this case is a pneumatic
tyre.
As evident from the longitudinal section of Fig. 3 the
core filament 3 surrounded by the wire filaments 2 has
contracted during vulcanization so that in the region
of the cut edge 6 between the wire filaments 2 a cavity
has materialized into which the rubber blend of the
rubber item 5 to be reinforced has penetrated.
Due to this penetration in accordance with the
invention an intermeshing of the wire cord, more
particularly of the wire filaments 2 and the rubber
item 5 to be reinforced is achieved in the region of
the cut edge 6 so that a particularly good embedding
and connection of the wire cord 1 in the rubber item 5
to be reinforced exists.
In accordance with the invention good location of the
wire cord edge 6 in the rubber item 5 to be reinforced
is achieved whilst reducing the risk of corrosion at
the same time.
As the non-metallic material for the core filament 3 a
non-drawn aliphatic polyamide, more particularly non-
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drawn nylon is particularly suitable. On vulcanization
such a core filament 3 of a non-drawn nylon shrinks by
approximately 5 to 7~, as a result of which a
sufficiently large cavity materializes at the cut edge
6 of the wire cord 1 into which the rubber blend can
penetrate where it is able to enter into a firm bond
with the brass of the surface of the wire filaments 2.
